Time-delays in non-dissociative single-photoionization of molecular oxygen

The recent development of XUV light sources with attosecond duration has opened new avenues for experimentalists to probe electron dynamics in matter. So far, time-resolved measurements have been mostly achieved by using an attosecond pulse to trigger a given electronic process, and a phase-locked femtosecond field to probe its dynamics. The electron dynamics under scrutiny are thus unraveled by varying the time delay between the two pulses. Among the several procedures proposed to extract the dynamics from such pump-probe measurements, the RABBITT technique has proved to be very promising for accessing time delays in photoionization of atoms and molecules. In this work, we used this technique to unravel time delays in the non-dissociative single photoionization of molecular oxygen. A COLTRIMS system was used to capture the full 3D momentum picture of both the photoelectrons and photoions resulting from the interaction between the molecule and the attosecond radiation. From the RABBITT spectrogram generated by measuring the photoelectron energy spectrum associated to the molecular ion O₂⁺, relative time delays in ionization from several molecular states are retrieved. Our experimental results are supported by ab initio theoretical calculations guiding the feasibility of the retrieval of channel- and vibrationally-resolved photoemission delay observables.